Google is facing a growing staff revolt, including in its Australian office, over plans to build a censored search engine in China.

Known as Dragonfly, little has been shared officially about the project, but the search app would reportedly "blacklist sensitive queries" and filter websites blocked by the Chinese Government.

Google's plan to return search to China caused global controversy when it was first reported by The Intercept, and about 1,400 employees signed an internal petition protesting against the move in August.

But in a remarkable step for the company, which typically keeps a tight lid on internal disagreements, more than 200 Google staff today signed an open letter calling for Project Dragonfly to be cancelled and claiming it would enable "state surveillance".

"Our opposition to Dragonfly is not about China: we object to technologies that aid the powerful in oppressing the vulnerable, wherever they may be," the protesters wrote.

The letter states that employees have raised concerns for months, but have so far found the response of leadership "unsatisfactory".

A Google spokesperson declined to comment on the letter, but said the company's work had been exploratory.

"We are not close to launching a search product in China," she said.

A return to China

The protest letter follows an Amnesty International campaign that opposes the censored search project over concerns it would set a "dangerous precedent" for government crackdowns on freedom of expression globally.

If it proceeds, Project Dragonfly would end a stalemate for Google in China that has lasted eight years.

Between 2006 and 2010, the company offered its search services in the country. It withdrew citing political pressure and hacking threats against the Gmail accounts of human rights activists.

Despite the recent controversy, Google chief executive Sundar Pichai backed the new search project at the WIRED 25 Summit in October, suggesting it was time to revaluate that decision.

"We are compelled by our mission [to] provide information to everyone, and [China is] 20 per cent of the world's population," he said.

"People don't understand fully, but you're always balancing a set of values."

The political response in the United States to reports of Google's plans has been largely unfavourable, however.

In August, six US senators wrote to Mr Pichai describing Project Dragonfly as "deeply troubling".

"It is a coup for the Chinese Government and Communist Party to force Google — the biggest search engine in the world — to comply with their onerous censorship requirements, and sets a worrying precedent," they wrote.

Growing protests over projects

In a year of reckoning for Silicon Valley, technology industry heavyweights have been heavily scrutinised for failing to live up to its declared values of openness and equality.

In particular, the year has been marked by staff protests over controversial Google projects and concerns over the company's culture.

In early November, thousands of employees staged a walkout, decrying the company's treatment of sexual harassment claims and pay inequality, among other issues.

In April, staff also protested against the company's work with the Pentagon, and an artificial intelligence program known as Project Maven, focused on interpreting drone video imagery.

Diane Greene, CEO of Google Cloud, later said the company would not purse any further Project Maven contracts and Google released a set of artificial intelligence principles, stipulating it would not work on technologies whose principal purpose "is to cause or directly facilitate injury to people".

In the view of today's letter writers, however, the company still has far to go.

"After a year of disappointments including Project Maven, Dragonfly, and Google's support for abusers, we no longer believe this is the case," they wrote.

As a bottle-feeding mother, preparing for my first cyclone season as a mum was frustrating beyond belief. Here's why some researchers think I'm not alone and what you can do to prepare this storm season.